A wireless device (e.g., a cellular phone or a smartphone) in a wireless communication system may transmit and receive data for two-way communication. The wireless device may include a transmitter for data transmission and a receiver for data reception. For data transmission, the transmitter may modulate a radio frequency (RF) carrier signal with data to generate a modulated RF signal, amplify the modulated RF signal to generate a transmit RF signal having the proper output power level, and transmit the transmit RF signal via an antenna to a base station. For data reception, the receiver may obtain a received RF signal via the antenna and may amplify and process the received RF signal to recover data sent by the base station.
The wireless device may transmit and receive communication data through a communication medium. In one example, the communication medium may be a wireless communication medium where communication data are transmitted and received by communication devices according to a wireless communication protocol. Example wireless communication protocols may include IEEE 802.11 protocols (e.g., Wi-Fi) and BLUETOOTH® protocols according to the Bluetooth Special Interest Group. Moreover, example wireless communication protocols may further include Long Term Evolution or LTE. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). In some examples, LTE provides over-the-air wireless communication of high-speed data for mobile phones and data terminals.
Analog signals within the wireless devices may undergo amplification during various processing operations. Amplifiers are commonly used in these communication devices to provide signal amplification. Different types of amplifiers are available for different uses. For example, a wireless communication device such as a cellular phone may include a transmitter and a receiver for bi-directional communication. The transmitter may utilize a driver amplifier (DA) and a power amplifier (PA), the receiver may utilize a low noise amplifier (LNA), and the transmitter and receiver may utilize variable gain amplifiers (VGAs).
Various classes of amplifiers may be used for signal amplification. A “class A” amplifier operates in a linear region all the time and may have better linearity at the expense of greater power consumption. A “class B” amplifier typically employs two complementary output transistors, with each output transistor being turned on for half of the time and turned off for the other half of the time. Class B amplifiers may consume less power than class A amplifiers, but may be susceptible to crossover distortion caused when one of the output transistors turns off as the other output transistor turns on. A “class AB” amplifier may also employ two complementary output transistors (similar to a class B amplifier), albeit with each output transistor being turned on for more than half of the time in order to reduce crossover distortion. Thus, class AB amplifiers may provide a good compromise between linearity and power consumption.
Some class AB amplifiers may provide differential output signals. Controlling a common-mode voltage of the differential output signals may increase amplifier design complexity, operation, and/or cost. Thus, there is a need to improve common-mode voltage control of differential output signals associated with class AB amplifiers.